1. Field of the Invention
The present invention relates to compositions and methods for building three-dimensional objects and, more particularly, to phase change compositions and selective deposition modeling methods for building three-dimensional objects utilizing such compositions.
2. Description of the Related Art
The art of building three-dimensional objects using selective deposition modeling methods is a rapidly developing technology. In one known selective deposition modeling method, a phase change composition, i.e., a composition that is a solid at ambient temperature and a liquid at an elevated temperature above ambient temperature, is melted by heating and deposited in liquid form onto a build platform in a controlled environment to form a multi-layered three-dimensional object on a layer-by-layer basis. The composition is deposited onto the build platform using a modified ink jet print head having a multiplicity of nozzles, e.g., 352 nozzles. A computer program prescribes the configuration of each layer of the object and controls the nozzles from which material is deposited during the deposition of any given layer to meet that layer's configuration. The material of each layer at least partially solidifies as a successive layer of material is selectively deposited thereupon from the print head. In this manner, the object is formed layer-by-layer into a final object having a desired shape and cross-section.
3D Systems, Inc., the Assignee of the present invention, has previously developed apparatus, methods and compositions for the selective deposition modeling of three-dimensional objects as described above. Thus, PCT Patent Application No. WO 97-11835 to Earl et al., published Apr. 3, 1997, describes a rapid prototyping apparatus and method for building three-dimensional objects employing selective deposition modeling. PCT Patent Application No. WO 97-11837 to Leyden et al., published Apr. 3, 1997, describes computer methods and apparatus for manipulating object and object support data and controlling object build styles for use in building three-dimensional objects by selective deposition modeling. U.S. Pat. No. 5,855,836 to Leyden, et al. issued Jan. 5, 1999, discloses phase change compositions for use in building three-dimensional objects by selective deposition modeling techniques. The contents of each of the above-noted published applications are expressly incorporated herein by reference.
Phase change compositions possessing specific physical properties are desirable in order to avoid various problems that can arise during and after creation of an object by selective deposition modeling techniques. The currently existing problems in building three-dimensional objects using selective deposition modeling are many. Such problems include curling of the object upon or after formation, cohesive failure of the support structures concurrently built with the object to support the object during the build process, adhesive failure or breaks between different materials constituting the object, the formation of stress cracks in the object, and delamination of layers constituting the object.
Important physical properties of a suitable phase change composition which influence the above include jetting viscosity, thermal stability at the jetting viscosity, melting point, softening point and softening range, freezing or solidification point, toughness, hardness, tensile strength and elongation.
A variety of factors influence success or failure at different stages of the build process. Initially, various constraints are imposed at the dispensing or jetting point of the process. It is currently eminently desirable to increase the existing deposition rates of build compositions, i.e., to significantly increase the jetting rate or speed of deposition of the build compositions, which requires compositions that are thermally stable and low in viscosity at high temperatures. During the build process itself, it is important to avoid curling, cracking and delamination of the multi-layered object as it forms and solidifies layer-by-layer. Finally, it is important to provide a finished three-dimensional article having the requisite toughness such that the product does not break or crumble easily with handling and use.
Phase change compositions useful in building three-dimensional objects by selective deposition modeling must have an appropriate viscosity range at the temperature range at which jetting or deposition takes place, taking into account the particular ink jet print head used in the build apparatus. Such compositions must also have an appropriate melting point range and freezing point range within the temperature range used in the build process so as to expedite the build process while simultaneously avoiding the development of defects in the object being built.
There is a variety of challenges peculiar to building three-dimensional objects by selective deposition modeling. It is desirable to minimize or completely avoid each of these problems. Cohesive failure is one such problem. Cohesive failure is a break within the material itself after deposition and solidification. Adhesive failure is another concern. Adhesive failure is a break at the interface between different materials after deposition and solidification. Curl is a particularly vexing defect. Curl is the lifting of a deposited multi-layered object in the Z-direction, either during or after solidification, due to large differences in shrinkage stress transmitted from layer to layer of the deposited material. Typically, from about 10% to about 15% shrinkage can be observed in other selective deposition modeling compositions between the time of dispensing (dispensing or jetting temperature) and final formation of the multi-layered object (ambient or solid temperature). Such high shrinkage rates are unacceptable, since they result in severe defects in the formed object, including not only curl, but also stress cracks and delamination of object layers.
Stress cracking is fracturing of a multi-layered object in either the X-axis (Y-Z plane), or Y-axis (X-Z plane), during or after solidification, due to high shrinkage stress from layer to layer of the object, low cohesive strength of the material itself and/or the specific geometry of the object being built. Delamination is the separation of layers of an object in the Z-axis (X-Y plane) due to differences in the surface energy of deposited and solidified solid portions of the object and the surface tension of molten material being deposited onto those solid portions. Thermal meltdown, also known as thermal runaway, is yet another concern. Thermal runaway is the melting of deposited object layers into a puddle of liquid, which can result from a detrimentally low freezing point (solidification point) for the phase change composition.
The selective deposition modeling of three-dimensional objects has heretofore involved one or more of the above-described deficiencies to varying degrees. Phase change compositions used thus far in the selective deposition modeling of three-dimensional objects have proved lacking in terms of their optimal physical properties and the requisite toughness, hardness, elongation and lack of curl, crack and delamination of the finished objects. While a plethora of phase change compositions have been designed as hot melt ink compositions for two-dimensional printing, as disclosed for example in U.S. Pat. No. 4,889,560 to Jaeger, et al. issued Dec. 26, 1989, and U.S. Pat. No. 4,830,671 to Frihart et al. issued May 16, 1989, such compositions do not possess the requisite properties for successfully building three-dimensional objects by selective deposition modeling.
It is thus highly desirable and would be a significant advance in the art to develop phase change compositions that not only result in three-dimensional objects devoid of the above-described undesirable defects, but that also permit a significantly more rapid building of such objects than has heretofore been achieved.
Ranges and ratios may be combined and are by weight unless otherwise indicated. Temperatures are in degrees Celsius, unless otherwise indicated. All references to published information are herein incorporated by reference.